The present invention generally relates to industrial playback robots, and more particularly to an industrial playback robot which is provided with a driving device having an electric motor as a driving source thereof and can be taught for use in carrying out a painting operation and the like.
A reduction gear mechanism for reducing a rotational speed of an electric motor is provided within a driving device of an industrial robot, and the robot is operated by the repeated forward and backward rotations of the electric motor.
A playback robot must be taught before the robot can perform a normal repeating operation, and it must be possible to teach the robot by use of only a small operating force. For this reason, a clutch mechanism is provided between the electric motor and a member which is driven by the electric motor, together with the reduction gear mechanism. The clutch mechanism is normally in an engaged state (transmitting state) for rotationally driving the member, and is in a disengaged state (non-transmitting state) during the teaching operation. As a result, the teaching operation can be performed smoothly without moving the reduction gear mechanism, that is, in a state where a load introduced by the reduction gear mechanism is released.
The clutch mechanism may be of a type which uses a disc and a pad, or may be or a type which uses a clutch gear pair and separates one of the clutch gears from the other confronting clutch gear. When the clutch mechanism using the disc and the pad is employed in a part of the robot where a large torque is required, there is a problem in that this clutch mechanism becomes bulky. Hence, the clutch mechanism using the clutch gear pair is generally used in the robot.
The clutch gear of the clutch mechanism is fitted on a spline shaft which is an output shaft of the reduction gear mechanism, and the clutch gear is movable in an axial direction of the spline shaft but is not rotatable independently of the spline shaft. When the robot is operated, the clutch gear rotates unitarily with the spline shaft which rotates in forward and backward directions so as to transmit the rotation of the output shaft of the reduction gear mechanism to the robot.
Since a center hole of the clutch gear of the clutch mechanism is inserted with the spline shaft, there is play in a circumferential direction of the spline shaft at a part where the clutch gear is fitted. For this reason, a rotary play angle of the spline shaft, that is, a rotary angle required for the clutch gear to start rotation from a point where the spline shaft starts to rotate in a direction opposite to a direction in which the spline shaft had been rotating, is enlarged and is relatively large at a position separated from the center of the spline shaft. This rotary play angle of the spline shaft deteriorates the rotational accuracy of the output shaft of the driving device and the operating accuracy of the robot is accordingly deteriorated. In addition, there are problems in that the play generates contact noise and the durability of the driving device becomes poor because of the contact caused by the play.
On the other hand, equipments used in flammable gas must be provided with the so-called explosion-proof apparatus (or gas proof apparatus) in order to prevent the flammable gas from being ignited and ensure safety.
One example of the equipment used under such a flammable condition is a painting robot used for painting. A conventional explosion-proof apparatus provided in the painting robot comprises an airtight container for containing only the electric motor out of the electric motor, the reduction gear mechanism, the clutch mechanism and a position detecting mechanism which constitute the driving mechanism, and the airtight container isolates the electric motor from the flammable gas. Compressed air is supplied within the airtight container as a protecting gas for keeping the pressure inside the airtight container over the atmospheric pressure, so that the flammable gas is prevented from entering the airtight container even when the airtight container is damaged. As a result, the flammable gas is prevented from being ignited by sparks generated in the electric motor.
However, heat and sparks which cause ignition of the flammable gas may be generated in the reduction gear mechanism and the clutch mechanism. Hence, there is a problem from the point of view of the safety when the explosion-proof apparatus is designed to only isolate the electric motor from the flammable gas by the airtight container.